The present invention relates to a roller bearing such as a conical roller bearing and a cylindrical roller bearing and, in particular, to a roller bearing in which a collar portion for guiding a plurality of rollers in the circumferential direction of a ring is formed in the end portion of the ring.
Generally, in most of roller bearings such as a conical roller bearing and a cylindrical roller bearing, a collar portion for guiding a plurality of rollers in the circumferential direction of a ring is formed in the end portion of the ring, and the end face of the roller is slidingly contacted with the collar portion. In the roller bearing of this type, in case where the ring is rotated at a high speed, there is generated frictional heat between the collar portion and roller, thereby raising a possibility that seizure can occur in the collar portion and roller. Thus, it is necessary to reduce the frictional heat that is generated between the collar portion and roller. In view of this, conventionally, for example, there are known a roller bearing structured such that there are formed a smooth portion and a valley portion in the end face of the roller and part of lubricating oil can be stored in the valley portion (JP-A-7-42746), and a roller bearing in which a plurality of fine recessed portions are formed in the roller guide surface of a collar portion to be slidingly contacted with the roller (JP-A-6-241235).
However, in both of the above-mentioned conventional roller bearings, the end face of the roller and the roller guide surface of the collar portion must be worked specially, which results in an increase in the manufacturing costs of the roller bearings. By the way, as a measure to reduce the frictional heat without enforcing special working on the end face of the roller as well as on the roller guide surface of the collar portion, there is known one which is disclosed in JP-A-9-236131. In this case, however, the portion of the roller to be contacted with the collar portion varies greatly in shape, which also causes an increase in the manufacturing cost of the roller bearing.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional roller bearings. Accordingly, it is an object of the present invention to provide a roller bearing which can reduce the frictional heat occurring between the roller and collar portion without enforcing special working on the end face of the roller or on the roller guide surface of the collar portion as well as without changing the shape of the roller greatly.
In attaining the above object, according to a first aspect of the present invention, there is provided a roller bearing including a collar portion formed in the end portion of a ring for guiding a plurality of cylindrical rollers in the circumferential direction of the ring, wherein a diameter of each of the cylindrical roller is expressed as 2R, a position in which an end face of the cylindrical roller intersect with a center axial line of the cylindrical roller is expressed as an original point, a position distant from the original point by 0.65R in an outside diameter direction of the cylindrical roller is expressed as a first point, a position distant from the first point by 0.20R in the outside diameter direction of the cylindrical roller is expressed as a second point, a position distant from the second point by 0.0005R in the axial direction of the cylindrical roller is expressed as a third position, a position distant from the second point by 0.003R in the axial direction of the cylindrical roller is expressed as a fourth position, and the contact portion of the end face of the cylindrical roller to be slidingly contacted with the collar portion is ground so as to have a continuously curved shape in which the outer contour line of the section of the end face of the cylindrical roller passes through the first point and passes between the third and fourth positions.
Also, according to a second aspect of the present invention, there is provided a roller bearing including a collar portion formed in the end portion of a ring for guiding a plurality of conical rollers in the circumferential direction of the ring, wherein a diameter of the conical roller is expressed as 2R, a position in which an end face of each of the conical rollers intersects with the center axial line of the conical roller is expressed as an original point, a position distant from the original point by 0.65R in an outside diameter direction of the conical roller is expressed as a first point, a position distant from the first point by 0.20R in the outside diameter direction of the conical roller is expressed as a second point, a position distant from the second point by 0.0065R in the axial direction of the conical roller is expressed as a third position, a position distant from the second point by 0.01R in the axial direction of the conical roller is expressed as a fourth position, and the contact portion of the end face of the conical roller to be slidingly contacted with the collar portion is ground so as to have a continuously curved shape in which the outer contour line of the section of the end face of the conical roller passes through the first point and passes between the third and fourth positions.
Further, according to a third aspect of the present invention, in a roller bearing as set forth in the first or second aspect of the present invention, the longitudinal elastic coefficient of an elastic grindstone for finishing the end face of the roller is set in the range of 10 MPa to 500 MPa.
Still further, according to a fourth aspect of the present invention, there is provided a roller bearing including in an end portion of a ring a collar portion for guiding a plurality of cylindrical rollers in the circumferential direction of the ring, wherein a contact portion of an end face of the cylindrical roller to be slidingly contacted with the collar portion is ground so as to have a continuously curved shape in which the outer contour line of the end face contact portion at a section decreases as the outer contour line goes outwardly in the radius direction of the roller.
According to the above aspects of the present invention, the end face (roller guide surface) of the collar portion on its sliding contact side with the roller is generally formed open at a certain angle with respect to a surface perpendicular to the raceway surface of the ring in order to facilitate the introduction of lubricating oil into between the roller and the roller guide surface of the collar portion. Therefore, a point of intersection with a grinding relief portion formed in the roller guide surface of the collar portion is geometrically easiest to touch the end face of the roller. On the other hand, since the contact side of the roller end face to be slidingly contacted with the collar portion is formed at right angles to the outside diameter surface of the roller, a point of intersection between a connecting portion (chamfer portion), which connects the outside diameter surface of the roller with the end face of the roller, and the end face of the roller is geometrically easiest to touch the collar portion.
Also, since lubricating oil existing in a portion, where the end face of the roller and collar portion is contacted with each other, is pulled into a small clearance between them due to the viscosity thereof, the shape of the mutual contact portion between the roller end face and collar portion may preferably be formed to have a clearance before and behind the mutual contact portion. Especially, because the shape of the end face of the roller is formed as a continuously curved shape, there is eliminated the possibility that an oil film can be cut due to high surface pressure occurring locally in the mutual contact portion, thereby being able to produce the oil film positively. Thanks to this, the seizure resisting property of the roller bearing can be enhanced.
On the other hand, since the Young""s modulus (longitudinal elastic coefficient) of a grindstone used to grind the end face of the roller is set in the range of 10 MPa to 500 MPa, the contact portion of the roller end face to be slidingly contacted with the collar portion can be formed as a continuously smooth arc surface not as a flat surface. In this case, for example, when grinding the end face of the roller on a horizontal or vertical duplex head grinder, the arc-surface roller end face contact portion is held by and between two grindstones and also the support rigidity of grains forming the grindstones is small; and, therefore, in case where the quantity of interference between the roller end face and grindstone does not increase, the end face portion cannot be ground and thus it cannot be removed by grinding. Accordingly, while the grindstone is interfering with the roller end face, the interference area of the grindstone naturally spreads up to the roller chamfer portion. And, under such interference condition between the grindstone and roller end face, grinding starts in the connecting portion between the roller end face and chamfer portion in which the pressure becomes highest, and the grinding widens to the chamber portion and plane portion of the roller end face gradually and continuously, with the result that the shape of the roller end face finally obtained becomes a continuously curved shape. Thanks to this, in the sliding contact portion between the roller and collar portion, an oil film can be formed smoothly and positively, which makes it possible to enhance the seizure resisting property of the roller bearing.